Restrictive reuse for a wireless communication system

ABSTRACT

For restrictive reuse, each cell (or each sector) is assigned (1) a set of usable subbands that may be allocated to users in the cell and (2) a set of forbidden subbands that is not used. The usable and forbidden sets for each cell are orthogonal to one other. The usable set for each cell also overlaps the forbidden set for each neighboring cell. A user u in a cell x may be allocated subbands in the usable set for that cell. If user u observes/causes high level of interference from/to a neighboring cell y, then user u may be allocated subbands from a “restricted” set containing subbands included in both the usable set for cell x and the forbidden set for cell y. User u would then observe/cause no interference from/to cell y. The subband restriction may be extended to avoid interference from multiple neighboring cells.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 60/516,558, filed Oct. 30, 2003, and assigned to the assigneehereof and hereby expressly incorporated by reference herein.

BACKGROUND

I. Field

The present invention relates generally to communication, and morespecifically to data transmission in a wireless multiple-accesscommunication system.

II. Background

A wireless multiple-access system can concurrently support communicationfor multiple wireless terminals on the forward and reverse links. Theforward link (or downlink) refers to the communication link from basestations to terminals, and the reverse link (or uplink) refers to thecommunication link from terminals to base stations. Multiple terminalsmay simultaneously transmit data on the reverse link and/or receive dataon the forward link. This may be achieved by multiplexing the datatransmissions on each link to be orthogonal to one another in time,frequency, and/or code domain. The orthogonality ensures that the datatransmission for each terminal does not interfere with the datatransmissions for other terminals.

A multiple-access system typically has many cells, where the term “cell”can refer to a base station and/or its coverage area depending on thecontext in which the term is used. Data transmissions for terminals inthe same cell may be sent using orthogonal multiplexing to avoid“intra-cell” interference. However, data transmissions for terminals indifferent cells may not be orthogonalized, in which case each terminalwould observe “inter-cell” interference from other cells. The inter-cellinterference may significantly degrade performance for certaindisadvantaged terminals observing high levels of interference.

To combat inter-cell interference, a wireless system may employ afrequency reuse scheme whereby not all frequency bands available in thesystem are used in each cell. For example, a system may employ a 7-cellreuse pattern and a reuse factor of K=7. For this system, the overallsystem bandwidth W is divided into seven equal frequency bands, and eachcell in a 7-cell cluster is assigned one of the seven frequency bands.Each cell uses only one frequency band, and every seventh cell reusesthe same frequency band. With this frequency reuse scheme, the samefrequency band is only reused in cells that are not adjacent to eachother, and the inter-cell interference observed in each cell is reducedrelative to the case in which all cells use the same frequency band.However, a large reuse factor (e.g., two or more) represents inefficientuse of the available system resources since each cell is able to useonly a fraction of the overall system bandwidth.

There is therefore a need in the art for techniques to reduce inter-cellinterference in a more efficient manner.

SUMMARY

Techniques to efficiently avoid or reduce interference from stronginterferers in a wireless communication system are described herein. Astrong interferer to a given user u may be a base station (on theforward link) or another user (on the reverse link). User u may also bea strong interferer to other users. A strong interference entity foruser u may be a strong interferer causing high interference to user uand/or a strong interferee observing high interference from or due touser u. Strong interference entities (or interferers/interferees, orsimply, interferers/ees) for each user may be identified as describedbelow. Users are allocated system resources (e.g., frequency subbands)that are orthogonal to those used by their strong interferers/ees andthus avoid interfering with one another. These techniques are called“restrictive reuse” techniques and may be used for various wirelesssystems and for both the forward and reverse links.

In an embodiment of restrictive reuse, each cell/sector is assigned (1)a set of usable subbands that may be allocated to users in thecell/sector and (2) a set of forbidden subbands that are not allocatedto the users in the cell/sector. The usable set and the forbidden setfor each cell/sector are orthogonal to one other. The usable set foreach cell/sector also overlaps the forbidden set for each neighboringcell/sector. A given user u in a cell/sector x may be allocated subbandsin the usable set for that cell/sector. If user u observes (or causes)high level of interference from (to) a neighboring cell/sector y, thenuser u may be allocated subbands from a “restricted” set that containssubbands included in both the usable set for cell/sector x and theforbidden set for cell/sector y. User u would then observe (cause) nointerference from (to) cell/sector y since the subbands allocated touser u are members of the forbidden set not used by cell/sector y. Thesubband restriction may be extended to avoid interference from multipleneighboring cells/sectors.

Various aspects and embodiments of the invention are described infurther detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and nature of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings in which like reference charactersidentify correspondingly throughout and wherein:

FIG. 1 shows a wireless multiple-access communication system;

FIGS. 2A and 2B show a sectorized cell and its model, respectively;

FIG. 3 shows an exemplary multi-cell layout with 3-sector cells;

FIG. 4 shows three overlapping forbidden sets for three sectors;

FIGS. 5A through 5D show four unrestricted and restricted sets for asector;

FIG. 6 shows an example for forming three forbidden subband sets;

FIGS. 7A through 7D show a distribution of four users in a cluster ofseven sectors and non-interference patterns for three of the users;

FIG. 8 shows a process for allocating subbands to users with restrictivereuse;

FIG. 9 shows a block diagram of a transmitting entity; and

FIG. 10 shows a block diagram of a receiving entity.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment or design described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs.

FIG. 1 shows a wireless multiple-access communication system 100. System100 includes a number of base stations 110 that support communicationfor a number of wireless terminals 120. A base station is a fixedstation used for communicating with the terminals and may also bereferred to as an access point, a Node B, or some other terminology.Terminals 120 are typically dispersed throughout the system, and eachterminal may be fixed or mobile. A terminal may also be referred to as amobile station, a user equipment (UE), a wireless communication device,or some other terminology. Each terminal may communicate with one orpossibly multiple base stations on the forward and reverse links at anygiven moment.

For a centralized architecture, a system controller 130 couples to thebase stations and provides coordination and control for these basestations. For a distributed architecture, the base stations maycommunicate with one another as needed, e.g., to serve a terminal,coordinate usage of system resources, and so on.

FIG. 2A shows a cell 210 with three sectors. Each base station providescommunication coverage for a respective geographic area. The coveragearea of each base station may be of any size and shape and is typicallydependent on various factors such as terrain, obstructions, and so on.To increase capacity, the base station coverage area may be partitionedinto three sectors 212 a, 212 b, and 212 c, which are labeled as sectors1, 2, and 3, respectively. Each sector may be defined by a respectiveantenna beam pattern, and the three beam patterns for the three sectorsmay point 120° from each other. The size and shape of each sector aregenerally dependent on the antenna beam pattern for that sector, and thesectors of the cell typically overlap at the edges. A cell/sector maynot be a contiguous region, and the cell/sector edge may be quitecomplex.

FIG. 2B shows a simple model for sectorized cell 210. Each of the threesectors in cell 210 is modeled by an ideal hexagon that approximates theboundary of the sector. The coverage area of each base station may berepresented by a clover of three ideal hexagons centered at the basestation.

Each sector is typically served by a base transceiver subsystem (BTS).In general, the term “sector” can refer to a BTS and/or its coveragearea, depending on the context in which the term is used. For asectorized cell, the base station for that cell typically includes theBTSs for all sectors of that cell. For simplicity, in the followingdescription, the term “base station” is used generically for both afixed station that serves a cell and a fixed station that serves asector. A “serving” base station or “serving” sector is one with which aterminal communicates. The terms “terminal” and “user” are also usedinterchangeably herein.

The restrictive reuse techniques may be used for various communicationsystems. For clarity, these techniques are described for an OrthogonalFrequency Division Multiple Access (OFDMA) system that utilizesorthogonal frequency division multiplexing (OFDM). OFDM effectivelypartitions the overall system bandwidth into a number of (N) orthogonalfrequency subbands, which are also referred to as tones, sub-carriers,bins, frequency channels, and so on. Each subband is associated with arespective sub-carrier that may be modulated with data.

In the OFDMA system, multiple orthogonal “traffic” channels may bedefined whereby (1) each subband is used for only one traffic channel inany given time interval and (2) each traffic channel may be assignedzero, one, or multiple subbands in each time interval. A traffic channelmay be viewed as a convenient way of expressing an assignment ofsubbands for different time intervals. Each terminal may be assigned adifferent traffic channel. For each sector, multiple data transmissionsmay be sent simultaneously on multiple traffic channels withoutinterfering with one another.

The OFDMA system may or may not use frequency hopping (FH). Withfrequency hopping, a data transmission hops from subband to subband in apseudo-random manner, which can provide frequency diversity and otherbenefits. For a frequency hopping OFDMA (FH-OFDMA) system, each trafficchannel may be associated with a specific FH sequence that indicates theparticular subband(s) to use for that traffic channel in each timeinterval (or hop period). The FH sequences for different trafficchannels in each sector are orthogonal to one another so that no twotraffic channels use the same subband in any given hop period. The FHsequences for each sector may also be pseudo-random with respect to theFH sequences for neighboring sectors. These properties for the FHsequences minimize intra-sector interference and randomize inter-sectorinterference.

In the OFDMA system, users with different channel conditions may bedistributed throughout the system. These users may have differentcontribution and tolerance to inter-sector interference. The channelcondition for each user may be quantified by a signal quality metric,which may be defined by a signal-to-interference-and-noise ratio (SINR),a channel gain, a received pilot power, and/or some other quantitymeasured for the user's serving base station, some other measurements,or any combination thereof. A weak user has a relatively poor signalquality metric (e.g., a low SINR) for its serving base station, e.g.,due to a low channel gain for its serving base station and/or highinter-sector interference. A weak user may in general be locatedanywhere within a sector but is typically located far away from theserving base station. In general, a weak user is less tolerant tointer-sector interference, causes more interference to users in othersectors, has poor performance, and may be a bottleneck in a system thatimposes a fairness requirement.

Restrictive reuse can avoid or reduce interference observed/caused byweak users. This may be achieved by determining the likely sources ofhigh inter-sector interference (or strong interferers) and/or the likelyvictims of high inter-sector interference (or strong interferees) forthe weak users. The strong interferers may be base stations (on theforward link) and/or users (on the reverse link) in neighboring sectors.The strong interferees may be users in neighboring sectors. In any case,the weak users are allocated subbands that are orthogonal to those usedby the strong interferers/ees.

In an embodiment of restrictive reuse, each sector x is assigned ausable subband set (denoted as U_(x)) and a forbidden or unused subbandset (denoted as F_(x)). The usable set contains subbands that may beallocated to the users in the sector. The forbidden set containssubbands that are not allocated to users in the sector. The usable setand the forbidden set for each sector are orthogonal or disjoint in thatno subband is included in both sets. The usable set for each sector alsooverlaps the forbidden set for each neighboring sector. The forbiddensets for multiple neighboring sectors may also overlap. The users ineach sector may be allocated subbands from the usable set as describedbelow.

Restrictive reuse may be used for systems composed of unsectorized cellsas well as systems composed of sectorized cells. For clarity,restrictive reuse is described below for an exemplary system composed of3-sector cells.

FIG. 3 shows an exemplary multi-cell layout 300 with each 3-sector cellbeing modeled by a clover of three hexagons. For this cell layout, eachsector is surrounded in the first tier (or the first ring) by sectorsthat are labeled differently from that sector. Thus, each sector 1 issurrounded by six sectors 2 and 3 in the first tier, each sector 2 issurrounded by six sectors 1 and 3, and each sector 3 is surrounded bysix sectors 1 and 2.

FIG. 4 shows a Venn diagram illustrating a formation of threeoverlapping sets of subbands, labeled as F₁, F₂ and F₃, which may beused as three forbidden subband sets. In this example, each forbiddenset overlaps with each of the other two forbidden sets (e.g., forbiddenset F₁ overlaps with each of forbidden sets F₂ and F₃). Because of theoverlapping, an intersection set operation on any two forbidden setsyields a non-empty set. This property may be expressed as follows:F₁₂=F₁∩F₂≠Θ, F₁₃=F₁∩F₃≠Θ, and F₂₃=F₂∩F₃≠Θ,  Eq (1)where “∩” denotes an intersection set operation;

-   -   F_(xy) is a set containing subbands that are members of both        sets F_(x) and F_(y); and    -   Θ denotes a null/empty set.        Each of the three forbidden sets F₁, F₂ and F₃ is a subset of a        full set Ω that contains all N total subbands, or F₁⊂Ω, F₂⊂Ω,        and F₃⊂Ω. For efficient utilization of the available subbands,        the three forbidden sets may also be defined such that there is        no overlap over all three sets, which may be expressed as:        F₁₂₃=F₁∩F₂∩F₃=Θ.  Eq (2)        The condition in equation (2) ensures that each subband is used        by at least one sector.

Three usable subband sets U₁, U₂ and U₃ may be formed based on the threeforbidden subband sets F₁, F₂ and F₃, respectively. Each usable setU_(x) may be formed by a difference set operation between the full set Ωand forbidden set F_(x), as follows:U₁=Ω\F₁, U₂=Ω\F₂, and U₃=Ω\F₃,  Eq (3)where “\” denotes a difference set operation; and

-   -   U_(x) is a set containing subbands in the full set Ω that are        not in set F_(x).

The three sectors in each 3-sector cell may be assigned a different pairof usable set and forbidden set. For example, sector 1 may be assignedusable set U₁ and forbidden set F₁, sector 2 may be assigned usable setU₂ and forbidden set F₂, and sector 3 may be assigned usable set U₃ andforbidden set F₃. Each sector is also aware of the forbidden setsassigned to neighboring sectors. Thus, sector 1 is aware of forbiddensets F₂ and F₃ assigned to neighboring sectors 2 and 3, sector 2 isaware of forbidden sets F₁ and F₃ assigned to neighboring sectors 1 and3, and sector 3 is aware of forbidden sets F₁ and F₂ assigned toneighboring sectors 1 and 2.

FIG. 5A shows a Venn diagram for the usable set U₁ assigned to sector 1.Usable set U₁ (shown by diagonal hashing) includes all of the N totalsubbands except for those in the forbidden set F₁.

FIG. 5B shows a Venn diagram for a restricted usable set U₁₋₂ (shown bycross-hashing) for sector 1. Restricted set U₁₋₂ contains subbandsincluded in both the usable set U₁ for sector 1 and the forbidden set F₂for sector 2. Since the subbands in forbidden set F₂ are not used bysector 2, the subbands in restricted set U₁₋₂ are free of interferencefrom sector 2.

FIG. 5C shows a Venn diagram for a restricted usable set U₁₋₃ (shown byvertical hashing) for sector 1. Restricted set U₁₋₃ contains subbandsincluded in both the usable set U₁ for sector 1 and the forbidden set F₃for sector 3. Since the subbands in forbidden set F₃ are not used bysector 3, the subbands in restricted set U₁₋₃ are free of interferencefrom sector 3.

FIG. 5D shows a Venn diagram for a more restricted usable set U₁₋₂₃(shown by solid fill) for sector 1. Restricted set U₁₋₂₃ containssubbands included in all three of the usable set U₁ for sector 1, theforbidden set F₂ for sector 2, and the forbidden set F₃ for sector 3.Since the subbands in forbidden sets F₂ and F₃ are not used by sectors 2and 3, respectively, the subbands in restricted set U₁₋₂₃ are free ofinterference from both sectors 2 and 3.

As shown in FIGS. 5A through 5D, the restricted usable sets U₁₋₂, U₁₋₃and U₁₋₂₃ are different subsets of the unrestricted usable set U₁assigned to sector 1. Restricted usable sets U₂₋₁, U₂₋₃ and U₂₋₁₃ may beformed for sector 2, and restricted usable sets U₃₋₁, U₃₋₂ and U₃₋₁₂ maybe formed for sector 3 in similar manner. Table 1 lists the varioususable subband sets for the three sectors and the manner in which thesesets may be formed. The “reuse” sets in Table 1 are described below.

TABLE 1 Reuse Set Usable Subband Sets Description (1) U₁ = Ω\F₁Main/unrestricted usable set for sector 1 (1, 2) U₁₋₂ = U₁∩F₂ =F₂\(F₁∩F₂) Restricted usable set with no interference from sector 2 (1,3) U₁₋₃ = U₁∩F₃ = F₃\(F₁∩F₃) Restricted usable set with no interferencefrom sector 3 (1, 2, 3) U_(1-2,3) = U₁∩F₂∩F₃ = F₂∩F₃ More restrictedusable set with no interference from sectors 2 & 3 (2) U₂ = Ω\F₂Main/unrestricted usable set for sector 2 (2, 1) U₂₋₁ = U₂∩F₁ =F₁\(F₁∩F₂) Restricted usable set with no interference from sector 1 (2,3) U₂₋₃ = U₂∩F₃ = F₃\(F₂∩F₃) Restricted usable set with no interferencefrom sector 3 (2, 1, 3) U_(2-1,3) = U₂∩F₁∩F₃ = F₁∩F₃ More restrictedusable set with no interference from sectors 1 & 3 (3) U₃ = Ω\F₃Main/unrestricted usable set for sector 3 (3, 1) U₃₋₁ = U₃∩F₁ =F₁\(F₁∩F₃) Restricted usable set with no interference from sector 1 (3,2) U₃₋₂ = U₃∩F₂ = F₂\(F₂∩F₃) Restricted usable set with no interferencefrom sector 2 (3, 1, 2) U_(3-1,2) = U₃∩F₁∩F₂ = F₁∩F₂ More restrictedusable set with no interference from sectors 1 & 2

Each sector x (where x=1, 2, or 3) may allocate subbands in its usableset U_(x) to users in the sector by taking into account the users'channel conditions so that reasonably good performance may be achievedfor all users. Sector x may have weak users as well as strong users. Astrong user has a relatively good signal quality metric for its servingbase station and is typically more tolerant to higher level ofinter-sector interference. A weak user is less tolerant to inter-sectorinterference. Sector x may allocate any of the subbands in its usableset U_(x) to the strong users in the sector. Sector x may allocatesubbands in the restricted sets to the weak users in the sector. Theweak users are, in effect, restricted to certain subbands known to befree of interference from strong interfering sectors.

For example, a given user u in sector x may be allocated subbands fromusable set U_(x) for sector x. If user u is deemed to beobserving/causing high inter-sector interference from/to sector y, wherey≠x, then user u may be allocated subbands from the restricted setU_(x-y)=U_(x)∩F_(y). If user u is further deemed to be observing/causinghigh inter-sector interference from/to sector z, where z≠x and z≠y, thenuser u may be allocated subbands from the more restricted setU_(x-yz)=U_(x)∩F_(y)∩F_(z).

FIG. 6 shows an example for forming the three forbidden subband sets F₁,F₂ and F₃. In this example, the N total subbands are partitioned into Qgroups, with each group containing 3·L subbands that are given indicesof 1 through 3L, where Q≧1 and L>1. Forbidden set F₁ contains subbands1, L+1, and 2L+1 in each group. Forbidden set F₂ contains subbands 1,L+2, and 2L+2 in each group. Forbidden set F₃ contains subbands 2, L+1,and 2L+2 in each group. Set F₁₂ then contains subband 1 in each group,set F₁₃ contains subband L+1 in each group, and set F₂₃ contains subband2L+2 in each group.

In general, each forbidden set may contain any number of subbands andany one of the N total subbands, subject to the constraints shown inequation (1) and possibly (2). To obtain frequency diversity, eachforbidden set may contain subbands taken from across the N totalsubbands. The subbands in each forbidden set may be distributed acrossthe N total subbands based on a predetermined pattern, as shown in FIG.6. Alternatively, the subbands in each forbidden set may bepseudo-randomly distributed across the N total subbands. The threeforbidden sets F₁, F₂ and F₃ may also be defined with any amount ofoverlap. The amount of overlap may be dependent on various factors suchas, for example, the desired effective reuse factor for each sector(described below), the expected number of weak users in each sector, andso on. The three forbidden sets may overlap each other by the sameamount, as shown in FIG. 4, or by different amounts.

Each user may be associated with a “reuse” set that contains the servingsector for the user as well as strong interferers/ees, if any, for theuser. The serving sector is denoted by boldfaced and underlined text inthe reuse set. The strong interferers/ees are denoted by normal text,after the boldfaced and underlined text for the serving sector, in thereuse set. For example, a reuse set of (2, 1, 3) denotes sector 2 beingthe serving sector and sectors 1 and 3 being strong interferers/ees.

Strong interferers to a given user u on the forward link are typicallyfixed and may be specifically identified, e.g., based on pilotstransmitted by the sectors. Strong interferers to user u on the reverselink may not be easily identified by forward link measurement performedby user u and may be deduced, e.g., based on reverse link interferencemeasurement by the serving base station of user u. Strong interfereesfor user u may also be specifically identified or deduced. Stronginterferers/ees for each user may be determined in various manners.

In one embodiment, strong interferers/ees for a given user u aredetermined based on received pilot powers, as measured by user u, fordifferent sectors. Each sector may transmit a pilot on the forward linkfor various purposes such as signal detection, timing and frequencysynchronization, channel estimation, and so on. User u may search forpilots transmitted by the sectors and measure the received power of eachdetected pilot. User u may then compare the received pilot power foreach detected sector against a power threshold and add the sector to itsreuse set if the received pilot power for the sector exceeds the powerthreshold.

In another embodiment, strong interferers/ees for user u are determinedbased on an “active” set maintained by user u. The active set containsall sectors that are candidates for serving user u. A sector may beadded to the active set, e.g., if the received pilot power for thesector, as measured by user u, exceeds an add threshold (which may ormay not be equal to the power threshold described above). Each user inthe system may be required to (e.g., periodically) update its active setand to report the active set to its serving sector. The active setinformation may be readily available at the sector and may be used forrestrictive reuse.

In yet another embodiment, strong interferers/ees for user u aredetermined based on received pilot powers, as measured at differentsectors, for user u. Each user may also transmit a pilot on the reverselink for various purposes. Each sector may search for pilots transmittedby users in the system and measure the received power of each detectedpilot. Each sector may then compare the received pilot power for eachdetected user against the power threshold and inform the user's servingsector if the received pilot power exceeds the power threshold. Theserving sector for each user may then add sectors that have reportedhigh received pilot powers to that user's reuse set.

In yet another embodiment, strong interferers/ees for user u aredetermined based on a position estimate for user U. The position of useru may be estimated for various reasons (e.g., to provide locationservice to user u) and using various position determination techniques(e.g., Global Positioning System (GPS), Advanced Forward LinkTrilateration (A-FLT), and so on, which are known in the art). Thestrong interferers/ees for user u may then be determined based on theposition estimate for user u and sector/cell layout information.

Several embodiments for determining strong interferers/ees for each userhave been described above. Strong interferers/ees may also be determinedin other manners and/or based on other quantities besides received pilotpower. A good signal quality metric for determining strong interfererson the forward link is an average SINR measured at a user for a basestation, which is also called “geometry”. A good signal quality metricfor determining strong interferees on the reverse link is a channel gainmeasured at a user for a base station, since SINR measurement is notavailable at the user for the base station. A single reuse set may bemaintained for both the forward and reverse links, or separate sets maybe used for the two links. The same or different signal quality metricsmay be used to update the sectors in the reuse set for the forward andreverse links.

In general, strong interferers/ees may be specifically identified basedon direct measurements (e.g., for the forward link) or deduced based onrelated measurements, sector/cell layout, and/or other information(e.g., for the reverse link). For simplicity, the following descriptionassumes that each user is associated with a single reuse set thatcontains the serving sector and other sectors (if any) deemed to bestrong interferers/ees for the user.

In a well-designed system, a weak user should have a relatively fairsignal quality metric for at least one neighboring sector. This allowsthe weak user to be handed off from a current serving sector to aneighboring sector if necessary. Each such neighboring sector may bedeemed as a strong interferer/ee to the weak user and may be included inthe user's reuse set.

FIG. 7A shows an example distribution of four users in a cluster ofseven sectors. In this example, user 1 is located near the middle ofsector 1 and has a reuse set of (1). User 2 is located near the boundarybetween sectors 1 and 3 and has a reuse set of (1, 3). User 3 is alsolocated near the boundary between sectors 1 and 3 but has a reuse set of(3, 1). User 4 is located near the boundary of sectors 1, 2 and 3 andhas a reuse set of (1, 2, 3).

FIG. 7B shows a non-interference pattern for user 1 in FIG. 7A. User 1is allocated subbands in usable set U₁ since its reuse set is (1).Because users in sector 1 are allocated orthogonal subbands, user 1 doesnot interfere with other users in sector 1. However, usable set U₁ isnot orthogonal to usable sets U₂ and U₃ for sectors 2 and 3,respectively. Thus, user 1 observes interference from the sixneighboring sectors 2 and 3 in the first tier around sector 1. User 1typically observes interference from distant or weak interferers inthese six neighboring sectors because strong interferers (to sector1/user 1) in these neighboring sectors are allocated subbands (e.g., inrestricted sets U₂₋₁ and U₃₋₁) that are orthogonal to those in usableset U₁. The area where other users do not interfere with user 1 is shownby cross-hashing and covers sector 1 and the edges of other sectors thatneighbor sector 1 (since the users in these neighboring sectors 2 and 3may be assigned subbands that are not used by sector 1).

FIG. 7C shows a non-interference pattern for user 2 in FIG. 7A. User 2is allocated subbands in restricted set U₁₋₂₃=U₁∩F₃ since its reuse setis (1, 3). Because sector 3 does not use the subbands in its forbiddenset F₃, the subbands allocated to user 2 are orthogonal to the subbandsused by sector 3. Thus, user 2 does not observe any interference fromother users in sector 1 as well as users in sector 3. User 2 observesinterference from distant interferers in the three first-tierneighboring sectors 2. The area where other users do not interfere withuser 2 covers sectors 1 and 3 and the edges of sectors 2 that neighborsector 1 (for the reason noted above for FIG. 7B).

FIG. 7D shows a non-interference pattern for user 4 in FIG. 7A. User 4is allocated subbands in restricted set U₁₋₂₃=U₁∩F₂∩F₃ since its reuseset is (1, 2, 3). Because sectors 2 and 3 do not use the subbands intheir forbidden sets F₂ and F₃, respectively, the subbands allocated touser 4 are orthogonal to the subbands used by sectors 2 and 3. Thus,user 4 does not observe any interference from other users in sector 1 aswell as users in the six first-tier neighboring sectors 2 and 3. Thearea where other users do not interfere with user 4 covers sectors 1, 2and 3.

In FIG. 7A, users 2 and 3 are located in close proximity and would haveinterfered strongly with each other without restrictive reuse. Withrestrictive reuse, user 2 is allocated subbands in restricted setU₁₋₃=U₁∩F₃ since its reuse set is (1, 3), and user 3 is allocatedsubbands in restricted set U₃₋₁=U₃∩F₁ since its reuse set is (3, 1).Restricted sets U₁₋₃ and U₃₋₁ are mutually orthogonal since eachrestricted set U_(x-y) contains only subbands that are excluded from theusable set U_(y) of which the other restricted set U_(y-x) is a subset.Because users 2 and 3 are allocated subbands from orthogonal restrictedsets U₁₋₃ and U₃₋₁, respectively, these two users do not interfere withone another.

As shown in FIGS. 7A through 7D, the interference experienced by a userdecreases as the size of its reuse set increases. A user with a reuseset size of one (e.g., user 1 in FIG. 7B) is interfered by distantinterferers in six first-tier neighboring sectors. A user with a reuseset size of two (e.g., user 2 in FIG. 7C) is interfered by distantinterferers in three first-tier neighboring sectors. A user with a reuseset size of three is interfered by interferers in second-tier neighborsectors. In contrast, without restrictive reuse, all users in the systemwould be interfered by randomly distributed interferers from all sixfirst-tier neighboring sectors.

Restrictive reuse may be used to mitigate inter-sector interference forweak users on both the forward and reverse links. On the forward link, aweak user u in sector x may observe high inter-sector interference frombase stations for neighboring sectors that are in its reuse set. Weakuser u may be allocated subbands that are not used by these neighboringsectors and would then observe no interference from the base stationsfor these sectors. Restrictive reuse may thus directly improve the SINRsof individual weak user u.

On the reverse link, weak user u may observe high inter-sectorinterference from users in neighboring sectors that are in its reuseset. Weak user u may be allocated subbands that are not used by theseneighboring sectors and would then observe no interference from theusers in these sectors. Weak user u may also be a strong interferer tothe users in the neighboring sectors. Weak user u typically transmits ata high power level in order to improve its received SINR at its servingsector x. The high transmit power causes more interference to all usersin the neighboring sectors. By restricting weak user u to subbands notused by the neighboring sectors in the reuse set, weak user u wouldcause no interference to the users in these sectors.

When restrictive reuse is applied across the system, weak user u maybenefit from lower inter-sector interference on the reverse link even ifthe strong interferers to weak user u cannot be identified. Weak usersin neighboring sectors that have sector x in their reuse sets may bestrong interferers to weak user u as well as other users in sector x.These strong interferers may be allocated subbands that are not used bysector x and would then cause no interference to the users in sector x.User u may thus observe no inter-sector interference from these stronginterferers even though user u is not able to identify them. Restrictivereuse generally improves the SINRs of all weak users.

For both the forward and reverse links, restrictive reuse can avoid orreduce interference observed by weak users from strong interferers andthus improve the SINRs for the weak users. Restrictive reuse may reducethe variation in SINRs among users in the system. As a result, improvedcommunication coverage as well as higher overall system capacity may beachieved for the system.

FIG. 8 shows a flow diagram of a process 800 for allocating subbands tousers in a sector with restrictive reuse. Process 800 may be performedby/for each sector. Initially, strong “interference entities”, if any,for each user in the sector are identified (block 812). A stronginterference entity for a given user u may be (1) a strong interferercausing high interference to user u and/or (2) a strong interfereeobserving high interference from or due to user u. A strong interferenceentity for user u may thus be (1) a base station causing highinterference to user u on the forward link, (2) another user causinghigh interference to user u on the reverse link, (3) a base stationobserving high interference from user u on the reverse link, (4) anotheruser observing high interference from user u's serving base station onthe forward link, or (5) some other entity for which mitigation ofinterference with user u is sought. The strong interference entities maybe identified based on, e.g., received pilot powers measured by the userfor different sectors, received pilot powers measured by differentsectors for the user, and so on. The strong interference entities foreach user may be included in the user's reuse set, as described above.In any case, a restricted usable set is determined for each user with atleast one strong interference entity (block 814). The restricted set foreach user may be obtained by performing an intersection set operation onthe usable set for the user's serving sector with the forbidden set foreach strong interference entity, or U_(x-y . . .) =U_(x)∩F_(y) . . . .Each user with at least one strong interference entity is allocatedsubbands in the restricted set determined for that user (block 816).Each user without a strong interference entity is allocated remainingsubbands in the usable set for the sector (block 818). The process thenterminates.

Process 800 shows allocation of subbands to weak users with at least onestrong interference entity first, then allocation of remaining subbandsto strong users. In general, the weak and strong users may be allocatedsubbands in any order. For example, users may be allocated subbandsbased on their priority, which may be determined from various factorssuch as the SINRs achieved by the users, the data rates supported by theusers, the payload size, the type of data to be sent, the amount ofdelay already experienced by the users, outage probability, the maximumavailable transmit power, the type of data services being offered, andso on. These various factors may be given appropriate weights and usedto prioritize the users. The users may then be allocated subbands basedon their priority.

Process 800 may be performed by each sector in each scheduling interval,which may be a predetermined time interval. Each sector may sendsignaling (e.g., to all users or to only users allocated differentsubbands) to indicate the subbands allocated to each user. Process 800may also be performed (1) whenever there is a change in users in thesector (e.g., if a new user is added or a current user is removed), (2)whenever the channel conditions for the users change (e.g., whenever thereuse set for a user changes), or (3) at any time and/or due to anytriggering criterion. At any given moment, all of the subbands may notbe available for scheduling, e.g., some subbands may already be in usefor retransmissions or some other purposes.

The forbidden sets represent overhead for supporting restrictive reuse.Since the subbands in forbidden set F_(x) are not used by sector x, thepercentage of the total subbands usable by sector x, which is also theeffective reuse factor for sector x, may be given as:|U_(x)|/|Ω|=(|Ω|−|F_(x)|)/|Ω|, where |U_(x)| denotes the size of U_(x).To reduce the amount of overhead for restrictive reuse, the forbiddensets may be defined to be as small as possible. However, the sizes ofthe restricted sets are dependent on the sizes of the forbidden sets.Thus, the forbidden sets may be defined based on expected requirementsfor weak users and possibly other factors.

The usable and forbidden sets may be defined in various manners. In oneembodiment, the usable and forbidden sets are defined based on globalfrequency planning for the system and remain static. Each sector isassigned a usable set and a forbidden set, forms its restricted sets asdescribed above, and thereafter uses the usable and restricted sets.This embodiment simplifies implementation for restrictive reuse sinceeach sector can act autonomously, and no signaling between neighboringsectors is required. In a second embodiment, the usable and forbiddensets may be dynamically defined based on sector loading and possiblyother factors. For example, the forbidden set for each sector may bedependent on the number of weak users in neighboring sectors, which maychange over time. A designated sector or a system entity (e.g., systemcontroller 130) may receive loading information for various sectors,define the usable and forbidden sets, and assign the sets to thesectors. This embodiment may allow for better utilization of systemresources based on the distribution of users. In yet another embodiment,the sectors may send inter-sector messages to negotiate the usable andforbidden sets.

Restrictive reuse can support handoff, which refers to the transfer of auser from a current serving base station to another base station that isdeemed better. Handoff may be performed as needed to maintain goodchannel conditions for users on the edge of sector coverage (or“sector-edge” users). Some conventional systems (e.g., a Time DivisionMultiple Access (TDMA) system) support “hard” handoff whereby a userfirst breaks away from the current serving base station and thenswitches to a new serving base station. A Code Division Multiple Access(CDMA) system supports “soft” and “softer” handoffs, which allow a userto simultaneously communicate with multiple cells (for soft handoff) ormultiple sectors (for softer handoff). Soft and softer handoffs canprovide additional mitigation against fast fading.

Restrictive reuse can reduce interference for sector-edge users, whichare good candidates for handoff. Restrictive reuse can also supporthard, soft, and softer handoffs. A sector-edge user u in sector x may beallocated subbands in the restricted set U_(x-y), which is free ofinterference from neighboring sector y. Sector-edge user u may alsocommunicate with sector y via subbands in the restricted set U_(y-x),which is free of interference from sector x. Since the restricted setsU_(x-y) and U_(y-x) are disjoint, user u may simultaneously communicatewith both sectors x and y (and with no interference from stronginterferers in both sectors) for soft or softer handoff. User u may alsoperform hard handoff from sector x to sector y. Since restricted setsU_(x-y) and U_(y-x) are absent of strong interferers from sectors y andx, respectively, the received SINR of user u may not change quite asabruptly when user u is handed off from sector x to sector y, which canensure a smooth handoff.

Power control may or may not be used in combination with restrictivereuse. Power control adjusts the transmit power for a data transmissionsuch that the received SINR for the transmission is maintained at atarget SINR, which may in turn be adjusted to achieve a particular levelof performance, e.g., 1% packet error rate (PER). Power control may beused to adjust the amount of transmit power used for a given data rate,so that interference is minimized. Power control be used for certain(e.g., fixed rate) transmissions and omitted for other (e.g., variablerate) transmissions. Full transmit power may be used for a variable ratetransmission (such as a hybrid automatic retransmission (H-ARQ), whichis continual transmission of additional redundancy information for eachpacket until the packet is decoded correctly) in order to achieve thehighest rate possible for a given channel condition.

In the above embodiment for restrictive reuse, each sector is associatedwith one usable set and one forbidden set. Some other embodiments ofrestrictive reuse are described below.

In another embodiment of restrictive reuse, each sector x is assigned anunrestricted usable subband set U_(x) and a “limited use” subband setL_(x). The unrestricted usable set contains subbands that may beallocated to any users in the sector. The limited use set containssubbands having certain use restrictions such as, e.g., a lower transmitpower limit. Sets U_(x) and L_(x) may be formed in the manner describedabove for sets U_(x) and F_(x), respectively.

Each sector x may allocate the subbands in sets U_(x) and L_(x) bytaking into account the channel conditions for the users so that goodperformance may be achieved for all users. The subbands in set U_(x) maybe allocated to any user in sector x. Weak users in sector x may beallocated subbands in (1) a restricted set U_(x-y)=U_(x)∩L_(y), if highinterference is observed from neighboring sector y, (2) a restricted setU_(x-z)=U_(x)∩L_(z), if high interference is observed from neighboringsector z, or (3) a restricted set U_(x-yz)=U_(x)∩L_(y)∩L_(z), if highinterference is observed from neighboring sectors y and z. Strong usersin sector x may be allocated subbands in L_(x).

A strong user v in sector x has a good signal quality metric for itsserving sector x and may be allocated subbands in the limited use setL_(x). On the forward link, sector x may transmit at or below the lowerpower limit for set L_(x) to strong user v. On the reverse link, stronguser v may transmit at or below the lower power limit to serving sectorx. Good performance may be achieved for strong user v for both theforward and reverse links, even with the lower transmit power, becauseof the good signal quality metric achieved by strong user v for sectorx.

Strong user v typically has poor signal quality metrics for neighboringsectors. On the forward link, the lower transmit power used by sector xfor strong user v causes low (and typically tolerable) levels ofinterference to users in neighboring sectors. On the reverse link, thelower transmit power used by strong user v plus the lower channel gainsfor neighboring sectors result in low (and typically tolerable) levelsof interference to the users in the neighboring sectors.

In yet another embodiment of restrictive reuse, each reuse set isassociated with a sorted list of subband sets that may be used for thereuse set. Due to frequency planning restrictions, the bandwidth of somerestricted sets may be quite small, such as restricted set U₁₋₂₃ whichcorresponds to reuse set (1,2,3). Suppose user u observes highinterference from sectors 2 and 3 and is assigned to reuse set (1,2,3).Although user u will experience higher SINR due to reduced interference,the bandwidth loss resulting from a restriction to a small restrictedset U₁₋₂₃ may be detrimental in terms of the achievable throughput ofuser U. Hence, for users in reuse set (1,2,3), a sorted list of subbandsets with descending preference may be defined, e.g., (U₁₋₂₃, [U₁₋₂,U₁₋₃], U₁), where the subband sets within the square brackets have equalpreference. The users in reuse set (1,2,3) may then use largerbandwidth, if necessary, by using additional subband sets in the sortedlist associated with reuse set (1,2,3). For users in reuse set (1,2),the sorted list may be (U₁₋₂, U₁, U₁₋₃, U₁₋₂₃). For users in reuse set(1), the sorted list may be (U₁, [U₁₋₂, U₁₋₃], U₁₋₂₃). The sorted listfor each reuse set may be defined to (1) reduce the amount ofinterference observed by the users in the reuse set and/or (2) reducethe amount of interference caused by the users in the reuse set.

In still yet another embodiment of restrictive reuse, each sector x isassigned multiple (M) usable sets and multiple (e.g., M) forbidden sets.The number of usable sets may or may not be equal to the number offorbidden sets. As an example, multiple (M) pairs of usable andforbidden sets may be formed, with the usable set U_(x) and theforbidden set F_(x) in each pair being formed such that each of the Ntotal subbands is included in only set U_(x) or set F_(x), e.g.,Ω=U_(x)∪F_(x), where “∪” denotes a union set operation. However, ingeneral, the M usable sets and M forbidden sets may be formed in variousmanners.

For example, the M usable sets may be formed such that they aresuccessively smaller subsets of the largest usable set. Each sector maythen use the smallest possible usable set based on its loading. This mayreduce the total interference to neighboring sectors when the sector ispartially loaded. This may also increase the variation in theinterference observed by neighboring sectors, which may be exploited toimprove overall system performance.

The M forbidden sets may be formed such that they are non-overlapping.The number of weaker users in each sector and their data requirementsare typically not known a priori. Each sector may utilize as manyforbidden sets for neighboring sectors as required to support its weakusers. For example, sector x may utilize subbands in more forbidden setsfor sector y to provide higher data rates to one or more weak users insector x observing high interference from sector y, or to support moreof these weak users. The sectors may coordinate usage of the forbiddensets.

In general, each sector may be assigned any number of unrestrictedusable subband sets and any number of “constrained” subband sets. Aconstrained subband set may be a forbidden subband set or a limited usesubband set. As an example, a sector may be assigned multipleconstrained subband sets. One constrained subband set may be a forbiddensubband set, and the remaining constrained subband set(s) may havedifferent transmit power limits and may be allocated to different tiersof strong users. As another example, a sector may be assigned multipleconstrained subband sets, where each constrained subband set may have adifferent transmit power limit (i.e., no forbidden set). The use ofmultiple usable and/or constrained sets for each sector may allow forbetter matching of subbands to weak users in different sectors.

For clarity, restrictive reuse has been specifically described for asystem with 3-sector cells. In general, restrictive reuse may be usedwith any reuse pattern. For a K-sector/cell reuse pattern, the forbiddenset for each sector/cell may be defined such that it overlaps with theforbidden set for each of the other K−1 sectors/cells, and may overlapwith different combinations of other forbidden sets. Each sector/cellmay form different restricted sets for different neighboring sectorsbased on its usable set and the forbidden sets for the neighboringsectors. Each sector/cell may then use the usable and restricted sets asdescribed above.

Restrictive reuse has also been described for an OFDMA system.Restrictive reuse may also be used for a TDMA system, a FrequencyDivision Multiple Access (FDMA) system, a CDMA system, a multi-carrierCDMA system, an Orthogonal Frequency Division Multiple Access (OFDMA)system, and so on. A TDMA system uses time division multiplexing (TDM),and transmissions for different users are orthogonalized by transmittingin different time intervals. An FDMA system uses frequency divisionmultiplexing (FDM), and transmissions for different users areorthogonalized by transmitting in different frequency channels orsubbands. In general, the system resources to be reused (e.g., frequencysubbands/channels, time slots, and so on) may be partitioned into usableand forbidden sets. The forbidden sets for neighboring sectors/cellsoverlap one another, as described above. Each sector may form restrictedsets based on its usable set and the forbidden sets for neighboringsectors/cells, as described above.

Restrictive reuse may be used for a Global System for MobileCommunications (GSM) system. A GSM system may operate in one or morefrequency bands. Each frequency band covers a specific range offrequencies and is divided into a number of 200 kHz radio frequency (RF)channels. Each RF channel is identified by a specific ARFCN (absoluteradio frequency channel number). For example, the GSM 900 frequency bandcovers ARFCNs 1 through 124, the GSM 1800 frequency band covers ARFCNs512 through 885, and the GSM 1900 frequency band covers ARFCNs 512through 810. Conventionally, each GSM cell is assigned a set of RFchannels and only transmits on the assigned RF channels. To reduceinter-cell interference, GSM cells located near each other are normallyassigned different sets of RF channels such that the transmissions forneighboring cells do not interfere with one another. GSM typicallyemploys a reuse factor greater than one (e.g., K=7).

Restrictive reuse may be used to improve efficiency and reduceinter-sector interference for a GSM system. The available RF channelsfor the GSM system may be used to form K pairs of usable and forbiddensets (e.g., K=7), and each GSM cell may be assigned one of the K setpairs. Each GSM cell may then allocate RF channels in its usable set tousers in the cell and RF channels in its restricted sets to weak users.Restrictive reuse allows each GSM cell to use a larger percentage of theavailable RF channels, and a reuse factor closer to one may be achieved.

Restrictive reuse may also be used for a multi-carrier communicationsystem that utilizes multiple “carriers” for data transmission. Eachcarrier is a sinusoidal signal that may be independently modulated withdata and is associated with a particular bandwidth. One such system is amulti-carrier IS-856 system (also called 3×-DO (data-only)) that hasmultiple 1.23 MHz carriers. Each sector/cell in the system may beallowed to use all carriers or only a subset of the carriers. Asector/cell may be forbidden to use a given carrier to avoid causinginterference on the carrier, which may allow other sectors/cells usingthis carrier to observe less (or no) interference, achieve higher SINR,and attain better performance. Alternatively, a sector/cell may beconstrained to use a lower transmit power limit on a given carrier toreduce interference on the carrier. For each sector, the constrained(forbidden or limited use) carrier(s) may be statically or dynamicallyassigned.

Each sector may assign its users to its usable carrier(s). Each sectormay also assign each user to a carrier in a manner to avoid stronginterferers/ees for the user. For example, if multiple usable carriersare available, then a user may be assigned one of the carriers havingless interference for the user (e.g., a carrier not used by a stronginterferer to the user).

The processing for data transmission and reception with restrictivereuse is dependent on system design. For clarity, exemplary transmittingand receiving entities in a frequency hopping OFDMA system for therestrictive reuse embodiment with a pair of usable and forbidden subbandsets for each sector are described below.

FIG. 9 shows a block diagram of an embodiment of a transmitting entity110 x, which may be the transmit portion of a base station or aterminal. Within transmitting entity 110 x, an encoder/modulator 914receives traffic/packet data from a data source 912 for a given user u,processes (e.g., encodes, interleaves, and modulates) the data based ona coding and modulation scheme selected for user u, and provides datasymbols, which are modulation symbols for data. Each modulation symbolis a complex value for a point in a signal constellation for theselected modulation scheme. A symbol-to-subband mapping unit 916provides the data symbols for user u onto the proper subbands determinedby an FH control, which is generated by an FH generator 940 based on thetraffic channel assigned to user u. FH generator 940 may be implementedwith look-up tables, pseudo-random number (PN) generators, and so on.Mapping unit 916 also provides pilot symbols on subbands used for pilottransmission and a signal value of zero for each subband not used forpilot or data transmission. For each OFDM symbol period, mapping unit916 provides N transmit symbols for the N total subbands, where eachtransmit symbol may be a data symbol, a pilot symbol, or a zero-signalvalue.

An OFDM modulator 920 receives N transmit symbols for each OFDM symbolperiod and generates a corresponding OFDM symbol. OFDM modulator 920typically includes an inverse fast Fourier transform (IFFT) unit and acyclic prefix generator. For each OFDM symbol period, the IFFT unittransforms the N transmit symbols to the time domain using an N-pointinverse FFT to obtain a “transformed” symbol that contains N time-domainchips. Each chip is a complex value to be transmitted in one chipperiod. The cyclic prefix generator then repeats a portion of eachtransformed symbol to form an OFDM symbol that contains N+C chips, whereC is the number of chips being repeated. The repeated portion is oftencalled a cyclic prefix and is used to combat inter-symbol interference(ISI) caused by frequency selective fading. An OFDM symbol periodcorresponds to the duration of one OFDM symbol, which is N+C chipperiods. OFDM modulator 920 provides a stream of OFDM symbols. Atransmitter unit (TMTR) 922 processes (e.g., converts to analog,filters, amplifies, and frequency upconverts) the OFDM symbol stream togenerate a modulated signal, which is transmitted from an antenna 924.

Controller 930 directs the operation at transmitting entity 110 x.Memory unit 932 provides storage for program codes and data used bycontroller 930.

FIG. 10 shows a block diagram of an embodiment of a receiving entity 120x, which may be the receive portion of a base station or a terminal. Oneor more modulated signals transmitted by one or more transmittingentities are received by an antenna 1012, and the received signal isprovided to and processed by a receiver unit (RCVR) 1014 to obtainsamples. The set of samples for one OFDM symbol period represents onereceived OFDM symbol. An OFDM demodulator (Demod) 1016 processes thesamples and provides received symbols, which are noisy estimates of thetransmit symbols sent by the transmitting entities. OFDM demodulator1016 typically includes a cyclic prefix removal unit and an FFT unit.The cyclic prefix removal unit removes the cyclic prefix in eachreceived OFDM symbol to obtain a received transformed symbol. The FFTunit transforms each received transformed symbol to the frequency domainwith an N-point FFT to obtain N received symbols for the N subbands. Asubband-to-symbol demapping unit 1018 obtains the N received symbols foreach OFDM symbol period and provides received symbols for the subbandsassigned to user u. These subbands are determined by an FH controlgenerated by an FH generator 1040 based on the traffic channel assignedto user u. A demodulator/decoder 1020 processes (e.g., demodulates,deinterleaves, and decodes) the received symbols for user u and providesdecoded data to a data sink 1022 for storage.

A controller 1030 directs the operation at receiving entity 120×. Amemory unit 1032 provides storage for program codes and data used bycontroller 1030.

For restrictive reuse, each sector (or a scheduler in the system)selects users for data transmission, identifies the stronginterferers/ees for the selected users, determines the usable orrestricted set for each selected user based on its stronginterferers/ees (if any), and allocates subbands (or assigns trafficchannels) from the proper sets to the selected users. Each sector thenprovides each user with its assigned traffic channel, e.g., viaover-the-air signaling. The transmitting and receiving entities for eachuser then perform the appropriate processing to transmit and receivedata on the subbands indicated by the assigned traffic channel.

The restrictive reuse techniques described herein may be implemented byvarious means. For example, these techniques may be implemented inhardware, software, or a combination thereof. For a hardwareimplementation, the processing units used to identify stronginterferers/ees, determine restricted sets, allocate subbands, processdata for transmission or reception, and perform other functions relatedto restrictive reuse may be implemented within one or more applicationspecific integrated circuits (ASICs), digital signal processors (DSPs),digital signal processing devices (DSPDs), programmable logic devices(PLDs), field programmable gate arrays (FPGAs), processors, controllers,micro-controllers, microprocessors, other electronic units designed toperform the functions described herein, or a combination thereof.

For a software implementation, the restrictive reuse techniques may beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The software codes may be storedin a memory unit (e.g., memory unit 932 in FIG. 9 or memory unit 1032 inFIG. 10) and executed by a processor (e.g., controller 930 in FIG. 9 or1030 in FIG. 10). The memory unit may be implemented within theprocessor or external to the processor.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method of allocating system resources in awireless communication system, comprising: identifying interferenceentities for each of at least one terminal, the at least one terminalcommunicating with a base station within a current cell/sector, eachinterference entity communicating in other cells/sectors with whichmitigation of interference associated therewith is sought, wherein thecurrent cell/sector is associated with a set of system resourcesincluding a set of usable system resources and a set of unusable systemresources, where the usable set of system resources for each cell/sectoroverlap with the unusable set of system resources of the othercells/sectors, and where the unusable set of system resources for eachcell/sector overlap with the unusable set of systems resources of theother cells/sectors, wherein there exist a plurality of restricted setsof system resources within the current cell/sector's set of usablesystem resources that comprise intersection(s) of the currentcell/sector's usable set of system resources and unusable sets of systemresources from the other cells/sectors; and allocating system resourceswithin the current cell/sector, either from the usable set or from oneor more of the restricted sets, to the at least one terminal based onthe interference entities-identified in the other cells/sectors for theat least one terminal.
 2. The method of claim 1, wherein eachinterference entity for each terminal is another base station deemed tocause interference to the terminal on a forward link.
 3. The method ofclaim 1, wherein each interference entity for each terminal is anotherbase station deemed to observe interference from the terminal on areverse link.
 4. The method of claim 1, wherein each interference entityfor each terminal is another terminal deemed to cause interference tothe terminal on a reverse link.
 5. The method of claim 1, wherein eachinterference entity is assigned a set of system resources that isunusable by the interference entity.
 6. The method of claim 5, furthercomprising: determining a set of system resources usable for each of theat least one terminal based on the set of usable system resourcesassigned to the current cell/sector and sets of system resourcesunusable by the interference entities, identified for the terminal, andwherein each terminal is allocated system resources from the set ofsystem resources usable for the terminal.
 7. The method of claim 5,further comprising: determining a list of resource sets for each of theat least one terminal, wherein the resource sets in the list for eachterminal are formed based on different combinations of the set of usablesystem resources assigned to the current cell/sector and sets of systemresources unusable by the interference entities, identified for theterminal, and wherein each terminal is allocated system resources fromthe resource sets in the list determined for the terminal.
 8. The methodof claim 7, wherein the resource sets in the list for each terminal areordered to reduce interference caused or observed by the terminal, andwherein each terminal is allocated system resources from one or more ofthe ordered resource sets in the list determined for the terminal. 9.The method of claim 1, wherein the current cell/sector is assigned a setof usable system resources and a set of constrained system resources,and wherein full transmit power is allowed for the usable systemresources and reduced transmit power is allowed for the constrainedsystem resources.
 10. The method of claim 1, wherein each terminal isassociated with a set containing interference entities, identified forthe terminal.
 11. The method of claim 1, wherein each interferenceentity for each terminal is determined based on a signal quality metricachieved by the terminal for the interference entity.
 12. The method ofclaim 1, wherein each interference entity for each terminal isdetermined based on received pilot power measured at the terminal forthe interference entity.
 13. The method of claim 1, wherein eachinterference entity for each terminal is determined based on a channelgain between the terminal and the interference entity.
 14. The method ofclaim 1, wherein each interference entity for each terminal isdetermined based on a signal-to-interference-and-noise ratio (SINR)achieved by the terminal for the interference entity.
 15. The method ofclaim 1, wherein the system resources allocated to the at least oneterminal are used for data transmission on a reverse link.
 16. Themethod of claim 1, wherein the system resources allocated to the atleast one terminal are used for data transmission on a forward link. 17.The method of claim 1, wherein the wireless communication systemutilizes orthogonal frequency division multiplexing (OFDM), and whereinthe system resources allocated to the at least one terminal arefrequency subbands obtained via OFDM.
 18. The method of claim 1, whereinthe system resources allocated to the at least one terminal are radiofrequency (RF) channels.
 19. The method of claim 1, wherein the wirelesscommunication system is an orthogonal frequency division multiple access(OFDMA) system utilizing frequency hopping.
 20. A method of allocatingfrequency subbands in a wireless communication system utilizingorthogonal frequency division multiplexing (OFDM), comprising:identifying other cells/sectors, for each of at least one terminals, theat least one terminal communicating with a base station within a currentcell/sector; determining a set of frequency subbands usable for each ofthe at least one terminal based on a set of usable frequency subbandsassigned to the current cell/sector and sets of frequency subbandsunusable by the other cells/sectors, identified for the terminal,wherein the current cell/sector is assigned a set of usable frequencysubbands and a set of unusable frequency subbands, where the usable setof frequency subbands for each cell/sector overlap with the unusable setof frequency subbands of the other cells/sectors, and where the unusableset of frequency subbands for each cell/sector may overlap with theunusable set of frequency subbands of the other cells/sectors, whereinthere exist a plurality of restricted sets of frequency subbands withinthe current cell/sector's usable set of frequency subbands that compriseintersection(s) of the current cell/sector's usable set of frequencysubbands and unusable sets of frequency subbands from the othercells/sectors; and allocating to each of the at least one terminalfrequency subbands selected from either the usable set or from one ormore of the restricted sets of frequency subbands within the currentcell/sector.
 21. The method of claim 20, wherein each neighboring basestation for each terminal is a base station deemed to cause interferenceto the terminal, observe interference from the terminal, or both causeinterference to and observe interference from the terminal.
 22. Themethod of claim 20, wherein each neighboring base station for eachterminal is identified based on received pilot power measured at theterminal for the neighboring base station.
 23. An apparatus operable toallocate system resources in a wireless communication system,comprising: a controller operative to identify interference entities,for each of at least one terminal, the at least one terminalcommunicating with a base station within a current cell/sector, eachinterference entity being an entity communicating in othercells/sectors, with which mitigation of interference associatedtherewith is sought, wherein the current cell/sector is associated witha set of system resources including a set of usable system resources anda set of unusable system resources, where the usable set of systemresources for each cell/sector overlap with the unusable set of systemresources of the other cells/sectors, and where the unusable set ofsystem resources for each cell/sector overlap with the unusable set ofsystems resources of the other cells/sectors, wherein there exist aplurality of restricted sets of system resources within the currentcell/sector's set of system resources that comprise intersection(s) ofthe current cell/sector's usable set of system resources and unusablesets of system resources from the other cells/sectors; and allocatesystem resources within the current cell/sector, either from the usableset or from one or more of the restricted sets, to the at least oneterminal based on the interference entities identified in the othercells/sectors for the at least one terminal.
 24. The apparatus of claim23, wherein each terminal is allocated system resources not used bythe-interference entities, identified for the terminal.
 25. Theapparatus of claim 23, wherein each interference entity for eachterminal is a base station deemed to cause interference to the terminal,observe interference from the terminal, or both cause interference toand observe interference from the terminal.
 26. The apparatus of claim23, wherein each interference entity for each terminal is determinedbased on received pilot power measured at the terminal for theinterference entity.
 27. An apparatus operable to allocate systemresources in a wireless communication system, comprising: means foridentifying interference entities, for each of at least one terminal,the at least one terminal communicating with a base station within acurrent cell/sector, each interference entity being an entitycommunicating in other cells/sectors, with which mitigation ofinterference associated therewith is sought; means for determining a setof system resources usable for each of the at least one terminal basedon a set of usable system resources assigned to the current cell/sectorand sets of system resources unusable by the interference entitiesidentified for the terminal, wherein the terminal is allocated systemresources from the set of system resources usable for the terminal,where the usable set of system resources available for each cell/sectoroverlap with the unusable set of system resources of the othercells/sectors, and where the unusable set of system resources for eachcell/sector overlap with the unusable set of systems resources of theother cells/sectors, wherein there exist a plurality of restricted setsof system resources within the current cell/sector's set of systemresources that comprise intersection(s) of the current cell/sector'susable set of system resources and unusable sets of system resourcesfrom the other cells/sectors; and means for allocating system resourceswithin the current cell/sector, either from the usable set or from oneor more of the restricted sets, to the at least one terminal based onthe interference entities, identified in the other cells/sectors for theat least one terminal.
 28. A method of processing data in a wirelesscommunication system, comprising: obtaining an allocation of systemresources for a terminal, wherein the terminal is in communication witha base station within a current cell/sector and is allocated systemresources from a set of system resources usable for the terminal, wherethe usable set of system resources available for the current cell/sectoroverlap with the unusable set of system resources of the othercells/sectors, and where the unusable set of system resources for thecurrent cell/sector overlap with the unusable set of systems resourcesof the other cells/sectors, wherein there exist a plurality ofrestricted sets of system resources within the current cell/sector's setof system resources that comprise intersection(s) of the currentcell/sector's usable set of system resources and unusable sets of systemresources from the other cells/sectors; and wherein the set of systemresources usable within the current cell/sector for the terminal isdetermined from either the usable set or from one or more of therestricted sets based on a set of usable system resources assigned tothe current cell/sector and on sets of system resources not used byinterference entities, identified for the terminal, and wherein eachinterference entity is an entity communicating in other cells/sectorsfor which mitigation of interference with the terminal is sought; andgenerating a control indicative of the system resources allocated to theterminal.
 29. The method of claim 28, further comprising: receiving adata transmission sent using the system resources allocated to theterminal; and processing the received data transmission in accordancewith the control.
 30. The method of claim 28, further comprising:processing data for transmission in accordance with the control; andsending a data transmission using the system resources allocated to theterminal.
 31. The method of claim 28, wherein the system utilizesorthogonal frequency division multiplexing (OFDM), and wherein thesystem resources allocated to the terminal comprise one or morefrequency subbands.
 32. The method of claim 31, wherein the systemutilizes frequency hopping, and wherein the control indicates differentsubbands to use for data transmission in different time intervals. 33.An apparatus in a wireless communication system, comprising: a processorconfigured to obtain an allocation of system resources for a terminal,wherein the terminal is in communication with a base station within acurrent cell/sector and is allocated system resources from a set ofsystem resources usable for the terminal associated with the currentcell/sector, where the usable set of system resources available for thecurrent cell/sector overlap with the unusable set of system resources ofthe other cells/sectors, and where the unusable set of system resourcesfor the current cell/sector overlap with the unusable set of systemsresources of the other cells/sectors, wherein there exist a plurality ofrestricted sets of system resources within the current cell/sector's setof system resources that comprise intersection(s) of the currentcell/sector's usable set of system resources and unusable sets of systemresources from the other cells/sectors, wherein the set of systemresources usable within the current cell/sector for the terminal arebased on either the usable set or from one or more of the restrictedsets of system resources not used by interference entities, identifiedfor the terminal, and wherein each interference entity is an entitycommunicating in other cells/sectors for which mitigation ofinterference with the terminal is sought, a generator operative togenerate a control indicative of the system resources allocated to theterminal; and a memory coupled to the processor for storing data. 34.The apparatus of claim 33, further comprising: a demodulator operativeto receive a data transmission sent using the system resources allocatedto the terminal; and a processing unit operative to process the receiveddata transmission in accordance with the control.
 35. The apparatus ofclaim 33, further comprising: a processing unit operative to processdata for transmission in accordance with the control; and a modulatoroperative to send a data transmission using the system resourcesallocated to the terminal.
 36. An apparatus in a wireless communicationsystem, comprising: means for obtaining an allocation of systemresources for a terminal, wherein the terminal is in communication witha base station within a current cell/sector, wherein the currentcell/sector is assigned a set of system resources including a set ofusable and unusable system resources, where the usable set of systemresources available for the current cell/sector overlap with theunusable set of system resources of the other cells/sectors, and wherethe unusable set of system resources for the current cell/sector overlapwith the unusable set of systems resources of the other cells/sectors,wherein there exist a plurality of restricted sets of system resourceswithin the current cell/sector's set of system resources that compriseintersection(s) of the current cell/sector's usable set of systemresources and unusable sets of system resources from the othercells/sectors, wherein the terminal is allocated system resources withinthe current cell/sector, either from the usable set or from one or moreof the restricted sets, not used by the interference entities,identified for the terminal, and wherein each interference entity is anentity communicating in other cells/sectors for which mitigation ofinterference with the terminal is sought; and means for generating acontrol indicative of the system resources allocated to the terminal.37. An apparatus operable to allocate frequency subbands in a wirelesscommunication system utilizing orthogonal frequency divisionmultiplexing (OFDM), comprising: a controller operative to: identifyother cells/sectors, for each of at least one terminal, the at least oneterminal communicating with a base station within a current cell/sector;determine a set of frequency subbands usable for each of the at leastone terminal based on a set of usable frequency subbands assigned to thecurrent cell/sector and sets of frequency subbands unusable by the othercells/sectors, identified for the terminal, wherein the currentcell/sector is assigned a set of usable frequency subbands and a set ofunusable frequency subbands, where the usable set of frequency subbandsfor each cell/sector overlap with the unusable set of frequency subbandsof the other cells/sectors, and where the unusable set of frequencysubbands for each cell/sector may overlap with the unusable set offrequency subbands of the other cells/sectors, wherein there exist aplurality of restricted sets of frequency subbands within the currentcell/sector's usable set of frequency subbands that compriseintersection(s) of the current cell/sector's usable set of frequencysubbands and unusable sets of frequency subbands from the othercells/sectors; and allocate to each of the at least one terminalfrequency subbands selected from either the usable set or from one ormore of the restricted sets of frequency subbands within the currentcell/sector.
 38. The apparatus of claim 37, wherein each neighboringbase station for each terminal is a base station deemed to causeinterference to the terminal, observe interference from the terminal, orboth cause interference to and observe interference from the terminal.39. The method of claim 37, wherein each neighboring base station foreach terminal is identified based on received pilot power measured atthe terminal for the neighboring base station.
 40. An apparatus operableto allocate frequency subbands in a wireless communication systemutilizing orthogonal frequency division multiplexing (OFDM), comprising:means for identifying other cells/sectors, for each of at least oneterminal, the at least one terminal communicating with a base stationwithin a current cell/sector; means for determining a set of frequencysubbands usable for each of the at least one terminal based on a set ofusable frequency subbands assigned to the current cell/sector and setsof frequency subbands unusable by the other cells/sectors, identifiedfor the terminal, wherein the current cell/sector is assigned a set ofusable frequency subbands and a set of unusable frequency subbands,where the usable set of frequency subbands for each cell/sector overlapwith the unusable set of frequency subbands of the other cells/sectors,and where the unusable set of frequency subbands for each cell/sectormay overlap with the unusable set of frequency subbands of the othercells/sectors, wherein there exist a plurality of restricted sets offrequency subbands within the current cell/sector's usable set offrequency subbands that comprise intersection(s) of the currentcell/sector's usable set of frequency subbands and unusable sets offrequency subbands from the other cells/sectors; and means forallocating to each of the at least one terminal frequency subbandsselected from either the usable set or from one or more of therestricted sets of frequency subbands within the current cell/sector.41. The method of claim 40, wherein each neighboring base station foreach terminal is a base station deemed to cause interference to theterminal, observe interference from the terminal, or both causeinterference to and observe interference from the terminal.
 42. Themethod of claim 40, wherein each neighboring base station for eachterminal is identified based on received pilot power measured at theterminal for the neighboring base station.
 43. An apparatus operable toallocate system resources in a wireless communication system,comprising: a processor; and a memory unit providing storage for programcodes executed by the processor to: identify interference entities foreach of at least one terminal, the at least one terminal communicatingwith a base station within a current cell/sector each interferenceentity communicating in other cells/sectors with which mitigation ofinterference associated therewith is sought, wherein the currentcell/sector is associated with a set of system resources including a setof usable system resources and a set of unusable system resources, wherethe usable set of system resources for each cell/sector overlap with theunusable set of system resources of the other cells/sectors, and wherethe unusable set of system resources for each cell/sector overlap withthe unusable set of systems resources of the other cells/sectors,wherein there exists a plurality of restricted sets of system resourceswithin the current cell/sector's set of usable system resources thatcomprise intersection(s) of the current cell/sector's usable set ofsystem resources and unusable sets of system resources from the othercells/sectors; and allocate system resources within the currentcell/sector, either from the usable set or from one or more of therestricted sets, to the at least one terminal based on the interferenceentities-identified in the other cells/sectors for the at least oneterminal.
 44. An apparatus operable to allocate frequency subbands in awireless communication system utilizing orthogonal frequency divisionmultiplexing (OFDM), comprising: a processor; and a memory unitproviding storage for program codes executed by the processor to:identify other cells/sectors, for each of at least one terminal, the atleast one terminal communicating with a base station within a currentcell/sector; determine a set of frequency subbands usable for each ofthe at least one terminal based on a set of usable frequency subbandsassigned to the current cell/sector and sets of frequency subbandsunusable by the other cells/sectors, identified for the terminal,wherein the current cell/sector is assigned a set of usable frequencysubbands and a set of unusable frequency subbands, where the usable setof frequency subbands for each cell/sector overlap with the unusable setof frequency subbands of the other cells/sectors, and where the unusableset of frequency subbands for each cell/sector may overlap with theunusable set of frequency subbands of the other cells/sectors, whereinthere exists a plurality of restricted sets of frequency subbands withinthe current cell/sector's usable set of frequency subbands that compriseintersection(s) of the current cell/sector's usable set of frequencysubbands and unusable sets of frequency subbands from the othercells/sectors; and allocate to each of the at least one terminalfrequency subbands selected from either the usable set or from one ormore of the restricted sets of frequency subbands within the currentcell/sector.
 45. An apparatus operable to process data in a wirelesscommunication system, comprising: a processor; and a memory unitproviding storage for program codes executed by the processor to: obtainan allocation of system resources for a terminal, wherein the terminalis in communication with a base station within a current cell/sector andis allocated system resources from a set of system resources usable forthe terminal, where the usable set of system resources available for thecurrent cell/sector overlap with the unusable set of system resources ofthe other cells/sectors, and where the unusable set of system resourcesfor the current cell/sector overlap with the unusable set of systemsresources of the other cells/sectors, wherein there exists a pluralityof restricted sets of system resources within the current cell/sector'sset of system resources that comprise intersection(s) of the currentcell/sector's usable set of system resources and unusable sets of systemresources from the other cells/sectors; and wherein the set of systemresources usable within the current cell/sector for the terminal isdetermined from either the usable set or from one or more of therestricted sets based on a set of usable system resources assigned tothe current cell/sector and on sets of system resources not used byinterference entities, identified for the terminal, and wherein eachinterference entity is an entity communicating in other cells/sectorsfor which mitigation of interference with the terminal is sought; andgenerate a control indicative of the system resources allocated to theterminal.
 46. A non-transitory computer-readable medium storing acomputer program, wherein the program contains instructions for:identifying interference entities for each of at least one terminal, theat least one terminal communicating with a base station within a currentcell/sector, each interference entity communicating in othercells/sectors with which mitigation of interference associated therewithis sought, wherein the current cell/sector is associated with a set ofsystem resources including a set of usable system resources and a set ofunusable system resources, where the usable set of system resources foreach cell/sector overlap with the unusable set of system resources ofthe other cells/sectors, and where the unusable set of system resourcesfor each cell/sector overlap with the unusable set of systems resourcesof the other cells/sectors, wherein there exist a plurality ofrestricted sets of system resources within the current cell/sector's setof usable system resources that comprise intersection(s) of the currentcell/sector's usable set of system resources and unusable sets of systemresources from the other cells/sectors; and allocating system resourceswithin the current cell/sector, either from the usable set or from oneor more of the restricted sets, to the at least one terminal based onthe interference entities-identified in the other cells/sectors for theat least one terminal.
 47. A non-transitory computer-readable mediumstoring a computer program, wherein the program contains instructionsfor: identifying other cells/sectors, for each of at least one terminal,the at least one terminal communicating with a base station within acurrent cell/sector; determining a set of frequency subbands usable foreach of the at least one terminal based on a set of usable frequencysubbands assigned to the current cell/sector and sets of frequencysubbands unusable by the other cells/sectors, identified for theterminal, wherein the current cell/sector is assigned a set of usablefrequency subbands and a set of unusable frequency subbands, where theusable set of frequency subbands for each cell/sector overlap with theunusable set of frequency subbands of the other cells/sectors, and wherethe unusable set of frequency subbands for each cell/sector may overlapwith the unusable set of frequency subbands of the other cells/sectors,wherein there exist a plurality of restricted sets of frequency subbandswithin the current cell/sector's usable set of frequency subbands thatcomprise intersection(s) of the current cell/sector's usable set offrequency subbands and unusable sets of frequency subbands from theother cells/sectors; and allocating to each of the at least one terminalfrequency subbands selected from either the usable set or from one ormore of the restricted sets of frequency subbands within the currentcell/sector.
 48. A non-transitory computer-readable medium storing acomputer program, wherein the program contains instructions for:obtaining an allocation of system resources for a terminal, wherein theterminal is in communication with a base station within a currentcell/sector and is allocated system resources from a set of systemresources usable for the terminal, where the usable set of systemresources available for the current cell/sector overlap with theunusable set of system resources of the other cells/sectors, and wherethe unusable set of system resources for the current cell/sector overlapwith the unusable set of systems resources of the other cells/sectors,wherein there exist a plurality of restricted sets of system resourceswithin the current cell/sector's set of system resources that compriseintersection(s) of the current cell/sector's usable set of systemresources and unusable sets of system resources from the othercells/sectors; and wherein the set of system resources usable within thecurrent cell/sector for the terminal is determined from either theusable set or from one or more of the restricted sets based on a set ofusable system resources assigned to the current cell/sector and on setsof system resources not used by interference entities, identified forthe terminal, and wherein each interference entity is an entitycommunicating in other cells/sectors for which mitigation ofinterference with the terminal is sought; and generating a controlindicative of the system resources allocated to the terminal.